λ/4 plates have been used for many applications and are already in use for reflection type LCDs, semi-transmission type LCDs, luminance improving films, pick-ups for optical discs or PS conversion devices. Most of the λ/4 plates currently used are phase difference plates in which optical anisotropy is developed by stretching a polymer film. The slow axis direction of a polymer film generally corresponds to the longitudinal direction or transverse direction of a sheet-type or roll-type film, and it is very difficult to prepare a polymer film having a slow axis at an oblique direction of the sheet or roll. In most cases where an optically anisotropic layer is used, the slow axis of the phase difference plate is disposed at an angle which is neither parallel nor orthogonal to the transmission axis of the polarizing plate. Further, each of the slow axes of two or more phase difference plates and the transmission axis of a polarizing plate is disposed at an angle which is not parallel to or orthogonal to each other in many cases. In general, the transmission axis of the polarizing plate is in a orthogonal direction to the longitudinal direction of the roll-type film, and thus in order to bond the phase difference plate with the polarizing plate, it is necessary to bond a chip obtained by cutting each film so as to become a predetermined angle. When a laminate of the phase difference plate and the polarizing plate is to be prepared by bonding the chip, a coating process of an adhesive, or a chip cutting or chip bonding process is required, making the treatment complicated, the deterioration in quality is easily caused by axial shift, reducing the yield and increasing costs, and foreign materials are also easily incorporated. In addition, in the polymer film, the development of the refractive index anisotropy in the 3-D direction is affected by various conditions such as stretching ratio, temperature, stretching speed and molecular weight of a polymer. Accordingly, it is also difficult to precisely control the optical anisotropy of the polymer film.
In order to solve the problem, proposed are phase difference plates having a slow axis at an angle which is neither parallel nor orthogonal to a roll-type film, in which an optical anisotropy is developed by coating a coating solution containing a discotic liquid crystal compound or a rod-like liquid crystal compound on the roll-type film to be arranged in a predetermined direction (Patent Documents 1 and 2). Furthermore, disclosed are phase difference plates which are aligned and fixed, such that the disc plane of the discotic liquid crystal molecule becomes substantially vertical to the film surface (Patent Documents 3, 4, 5, 6 and 7).
Further, although a configuration, in which an phase difference plate is used on the forefront as the phase difference plate on the forefront plane in an organic EL, a touch panel, a 3D display device and the like, has been proposed, in an phase difference plate in the related art, there are problems in that scratches easily occur, strength is insufficient, the reflection intensity of external light is high, light resistance is weak, foreign materials are easily attached and are not well detached, and the like, and thus it is not appropriate for the phase difference plate to be used on the forefront plane.